Patent GB-1308808-A (GB)
Title: Hydraulic driving device for sheet metal working presses
IPC: B30B15/24
Filed: 1970-03-23
Abstract: 1308808 Angular bending VERRINA SpA 23 March 1970 [29 March 1969] 13979/70 Heading B3E An hydraulic metal working press, e.g. a bending press, has an upper platen 7 lowered and raised by cylinders 6 and 9 respectively and co-axial compensating cylinders 13 for keeping the platen level during operation. Pistons 113 are mounted on a common piston rod 413, chambers 213 are connected respectively to the pressure chambers 209 of the return cylinders 9 and chambers 313 to a reservoir T. One is supplied by low and high pressure pumps P1 and P2 respectively, the pump P1 being connected to the reservoir T via a pressure limitation valve 12. In operation, oil is supplied by pumps P1 and P2 until the press tool contacts the workpiece when the valve 12 opens so that the platen is moved more slowly but with higher working pressure from the pump P2 only. The pistons 109 of return cylinders 9 are meanwhile moved downwardly, forcing oil into chambers 2, 3 of the compensating cylinders and moving the pistons 113 to the right, Fig, 3, oil from chambers 313 flowing back to the reservoir T via a pressure limitation valve 22. While the platen remains level the pressure in chambers 209 of both cylinders 9 and the chambers 213 of both cylinders 13 are equal to each other and correspond to the counter pressure in the chambers 313. If, for instance, the right hand end of the platen encounters greater mechanical resistance during lowering the pressure in the chambers 209 and 213 of the right hand chambers 9 and 13 respectively diminishes. The counter pressures in the two chambers 313 remain equal and the pressure in the chambers 209 and 213 of the left hand cylinder 9 and 13 rises to a degree equal to the drop in pressure at the right hand end of the platen and brakes the left hand end of the platen to the same degree as the mechanical resistance is braking the right hand end. Both pumps supply oil for the return stroke and the compensating cylinders act in inverse fashion to maintain the platen 7 level. In another embodiment, Fig. 4, not shown, the chambers 313 are connected to a fluid pressure chamber of a pressure accumulator (18) instead to the reservoir T via valve 22. In a further embodiment, Fig. 5, one pump P2 only is provided and feed cylinders act directly on the platen 7 or are as shown coaxial with the cylinders 6, the pistons 120 of the cylinders 20 being rigidly connected to the pistons 106 of cylinders 6 and being of smaller diameter than those pistons and the pistons 113 of cylinders 13. Instead of the chambers 209 of the return cylinders 9, the chambers 213 of cylinders 13 are connected to pressure chambers 220 of cylinders 20. In the feed line 17 to the cylinders 6 is an isolating valve 25 precontrolled by the pressure between that valve and the main operating valve V. The feed line 17 is connected to the reservoir T through a valve R3 which can be opened by the pressure in the return pipe 23 from cylinders 9. In operation, the valve 25 being closed, oil supplied by pump P2 is fed through valves V and R to chambers 313 of cylinders 13, forcing fluid into chamber 220 of the feed cylinders, thus lowering the platen 7 at high speed. Oil displaced from chambers 209 of return cylinders 9 flows to reservoir T and oil from the reservoir T opens valve R3 allowing oil to flow to chambers 206 of cylinders 6. The platen 7 is held level during its descent since the oil supply to cylinders 20 is controlled by the pistons 113 of compensating cylinders 13, the pressure decrease when one end encounters greater resistance than the other being balanced by an increase in pressure at the other end. When the platen contacts the workpiece pressure increase in the pipe F2 from pump P2 opens valve 25 to allow oil to be pumped direct to chambers 206 and increase working pressure on the platen. A still further embodiment, Fig. 6 (not shown), differs from that of Fig. 5 only in that return cylinders 9 are omitted and feed cylinders 20 are double acting.